Abstract

Oriented bounding box (OBB) bounding volume hierarchies offer a more precise fit than axis-aligned bounding box hierarchies in scenarios with thin elongated and arbitrarily rotated geometry, enhancing intersection test performance in ray tracing. However, determining optimally oriented bounding boxes can be computationally expensive and have high memory requirements. Recent research has shown that pre-built hierarchies can be efficiently converted to OBB hierarchies on the GPU in a bottom-up pass, yielding significant ray tracing traversal improvements. In this paper, we introduce a novel OBB construction technique where all internal node children share a consistent OBB transform, chosen from a fixed set of discrete quantized rotations. This allows for efficient encoding and reduces the computational complexity of OBB transformations. We further extend our approach to hierarchies with multiple children per node by leveraging Discrete Orientation Polytopes (k-DOPs), demonstrating improvements in traversal performance while limiting the build time impact for real-time applications. Our method is applied as a post-processing step, integrating seamlessly into existing hierarchy construction pipelines. Despite a 12.6% increase in build time, our experimental results demonstrate an average improvement of 18.5% in primary, 32.4% in secondary rays, and maximum gain of 65% in ray intersection performance, highlighting its potential for advancing real-time applications.

Acknowledgements

Special Thanks to Julien Beasley, Ryan Kennedy, John Tskok, Pratith Kanagaraj, Andreas Leitner, David McCalister, Pranabesh Sinha for your insights and contributions.